Because of the excellent directivity of laser, the power density of laser in the output direction is especially high, which greatly threatens human eyes. The wavelength of lasers used in the existing communication system is generally around 870 nm, 1310 nm and 1550 nm, which are all beyond the wavelength range of a visible light. Because it is invisible, the light beam has a greater possibility to hurt human eyes. After the inventions of Erbium-Doped Fiber Amplifier (EDFA) and Wavelength Division Multiplexing (WDM) techniques, the output power of optical signals carried in fibers is even higher than that of conventional Synchronous Digital Hierarchy (SDH) devices. In addition, such apparatuses as RAMAN amplifier may be introduced into the existing communication system, which makes the power of optical signals carried in fibers of some systems reach or even exceed 30 dBm. Such a high power of the optical signal greatly threatens safety of operators and maintenance personnel of telecommunication system.
The safety level of laser apparatus and device is defined in Standard IEC60825, which specifies the specific operational measure and safety identifier as well. The International Telecommunication Union-Telecommunication Standardization Sector (ITU-T) constitutes Standard G.664 for laser safety in communication system. According to the Standard G.664, an optical communication apparatus should be able to automatically reduce the output power to safe power and even turn off a laser when a laser leakage occurs. The solution is expressed as an Automatic Power Reduction (APR) and an Automatic Power Shutdown (APSD) solution in G.664.